Odd vessel

This rather odd looking vessel is currently operating a short way off shore at Littlehampton. It appears to be moving stuff (rocks, shingle or sand?) around fairly near the river mouth. There is a sand bar in that area that boats sometimes ground on so maybe it is to do with that.

They've chosen a fine day to do it on. The warm weather continues and it seems impossible to believe that it is October. What's next - snow?